Data from: Ecological forensics: using single point stable isotope values to infer seasonal schedules of animals after two diet switches

1.Animals adjust to seasonal challenges in physical, behavioural and spatial ways. Such adjustments are commonly associated with diet changes that often can be characterized isotopically.

2.We introduce the ‘double diet switch model’, with which the occurrence and timing of two subsequent diet switches of an individual animal can be traced with a single sample assayed for stable isotopes. We demonstrate the model for Sanderling, Calidris alba, a small shorebird that migrates from the Nearctic tundra breeding grounds to the intertidal flats of the Wadden Sea; during this migration some birds may stage in the North Atlantic areas.

3.The ‘double diet switch model’ successfully predicted the occurrence and timing of two diet switches in 59 Sanderlings captured in the Wadden Sea in July-September. Excluding birds that likely had over-summered at North Atlantic staging areas, the model predicted that Sanderlings departed from the Arctic on 13 July (range: 9-17 July), had a staging duration of 18.6 days in the North Atlantic, and arrived in the Wadden Sea on 1 August (31 July-1 August).The estimated mean Arctic departure dates coincided with the mean hatching date, suggesting that many individuals failed to produce young or left the care to a partner. Estimated mean arrival date matched the main arrival period in the Wadden Sea obtained from observation data. In this study we did not use lipid-free tissues, which may bias model predictions. After correcting for lipid components, the estimated departure date was 11 days later and the staging duration 8.5 days shorter, while arrival date was similar.

4.The ‘double diet switch model’ successfully identified the occurrence and timing of two subsequent diet switches. The ‘double diet switch model will not only apply to switches between three isotopic levels (as in the case study on Sanderling) but also to scenarios where the second switch reverses to the initial isotopic level. Due to this general applicability, the model can be adapted to a wide range of taxa and situations. Foreseeable applications include changes in habitat and food type, ontogenetic development, or drastic phenotypic changes such as the metamorphosis in insects and amphibians.

1. 动物会通过生理、行为及空间维度的适应性策略应对季节性生存挑战，这类调整通常与饮食变化相关，而饮食变化往往可通过同位素特征进行表征。
2. 本研究提出双饮食转换模型（double diet switch model），该模型可通过单份稳定同位素检测样本，追溯单只动物先后两次饮食转换的发生情况与时间节点。我们以三趾鹬（Calidris alba）为例验证该模型：这种小型滨鸟会从新北极冻原的繁殖地迁徙至瓦登海的潮间带滩涂，迁徙过程中部分个体可能在北大西洋区域中途停歇。
3. 双饮食转换模型成功预测了7-9月于瓦登海捕获的59只三趾鹬的两次饮食转换发生情况与时间节点。排除可能在北大西洋中途停歇地越夏的个体后，模型预测三趾鹬的北极迁出平均日期为7月13日（区间：7月9日-17日），在北大西洋的中途停歇时长为18.6天，并于8月1日（7月31日-8月1日）抵达瓦登海。估算的北极平均迁出日期与平均孵出日期重合，这表明多数个体未成功繁育，或仅将育幼职责交由配偶完成。估算的平均抵达日期与观测数据得到的瓦登海主要抵达时段相符。本研究未使用去脂组织，这可能对模型预测结果产生偏倚。在校正脂质成分后，估算的迁出日期延后11天，中途停歇时长缩短8.5天，而抵达日期无显著变化。
4. 双饮食转换模型可有效识别两次连续饮食转换的发生情况与时间节点。该模型不仅适用于三类同位素水平间的转换（如本研究中的三趾鹬案例），也可应用于第二次转换回归至初始同位素水平的场景。凭借这一普适性，该模型可适配绝大多数分类类群与研究场景。其潜在应用场景涵盖栖息地与食物类型的变化、个体发育过程，以及昆虫、两栖类的变态发育等剧烈表型改变。